That is not the way tire sizes work. The first number 245 is section width in milimeters. 245 mm This is the measured at the widest part of the tires side wall. Not a tread measurement. The /60 means 60 percent height to width ratio. 60 percent of 245 mm is the measurement from the rims edge to the top of the tires tread edge. Add that number twice, half above and half below the rim plus rim diameter. = total tire diameter.